The present invention relates to the field of mass storage devices. More particularly, this invention relates to a method of eliminating resonance in an actuator arm of a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer head to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer head is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of disc drive. Servo feedback information is used to accurately locate the transducer head. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
Quick and precise positioning requires the reduction of the vibration of the magnetic disc apparatus caused by the driving reaction force to the voice coil motor. What is needed is a disc drive which has is less susceptible to the reaction forces. This will improve settling characteristics after a seek from a first track on the disc to a target track on the disc and will improve track following operations of the disc drive. In other words, there is a need for a disc drive that has less relative motion between the actuator assembly and the base while under any type of servo control that requires corrections to be implemented with the voice coil motor. There is also a need for a static solution so that the resulting disc drive is more reliable over the life of the drive. Also needed is a device that can be assembled using current assembly techniques.
One constant goal associated with disc drives is to decrease or lessen the access time to data. Increasing the speed at which data can be retrieved is very desirable in a disc drive. The decrease in access time increases the speed at which a computer system can perform operations on data. When a computer is commanded to perform an operation on data or information that needs to be retrieved, the time necessary to retrieve the data from the disc is generally the bottleneck in the operation. When data is accessed more quickly, more transactions can generally be handled by a computer in a particular unit of time.
Most of the methods for controlling access time include referring to a seek profile. A seek profile is a pre-programmed equation or table which lists a desired velocity verses the stopping distance remaining until reaching the target track. In other words, a seek profile provides the velocity the transducer head should have at varying distances from the destination or target track and, at each of a succession of tracks terminating with the destination or target track. Generally, the seek profile (velocity) value is the highest possible value of velocity the actuator can have at a particular remaining distance to allow the actuator to be decelerated to a stop upon reaching the destination or target track. Of course, there may be factors, such as power savings, that may steer designers away from following the highest possible velocity.
The seek profile is shaped with respect to the number of tracks remaining in a seek to cause the transducer head to initially accelerate toward the destination or target track and subsequently decelerate to the destination or target track. In long seeks, these stages of the seek may be separated by a stage in which the transducer head traverses a series of tracks at a maximum speed that is selected on the basis of any of a number of criteria used by the manufacturer of the disc drive. For example, the maximum speed may be chosen to be the maximum speed the transducer head can attain with the power supply that is used to operate the servo system. A control signal is provided to the power amplifier that is directly proportional to the difference between the profile velocity and the actual velocity of the transducer head.
A typical seek is accomplished using closed loop control. The distance left to go to the destination or target track is determined and then the corresponding velocity from the velocity profile is selected. The difference between the actual actuator velocity and profile actuator velocity is provided to the servo controller. This value is then multiplied by a gain to give a control current output to the voice coil.
It is very crucial for the disc drives to have a smooth and clean seek settling, that is free from any resonance. This will generally help minimize missed revolutions and decrease access times and will also help in improving disc drive""s through-put performance. During manufacturing, disc drives found to have resonance in the actuator arms are rejected as disc drives having resonance are considered fatal error and therefore they are scrapped. This increases the production costs, and inconsistent throughput performance from disc drive to disc drive. Also the current compensation methods to overcome resonance in the disc drive actuator arms are not very effective, because the current methods require reducing the overall servo loop gain once the seek profile has been executed by the servo controller. It has been found that for disc drives having resonance problem, once an actuator arm is excited with the seek profile, it was difficult to eliminate the resonance by reducing the overall servo loop gain.
What is needed is a method to salvage disc drives having resonance, that reduces production costs, and improves throughput performance in the disc drives. What is also needed is a method to reduce resonance related noise in the disc drives having resonance problems, without having to reduce the overall servo loop gain after the seek profile has been executed by the servo controller.
A disc drive includes a base and a disc rotatably attached to the base. The disc drive also includes an actuator assembly rotatably attached to said base and a device for moving the actuator assembly. The actuator assembly includes a transducer head in a transducing relationship with respect to the disc. The disc drive includes a disc drive controller for controlling the movement of the actuator during track follow and track seek operations. The disc drive further includes a servo controller coupled to the actuator assembly for monitoring the actuator during seek operations. The disc drive controller further includes an analyzer, coupled to the servo controller for obtaining a maximum average settle time from the monitored settle times for each zone. Also included is a comparator, coupled to the analyzer and the servo controller to compare the maximum average settle time to a predetermined threshold value, and to issue a first command signal (indicating that the actuator arm will resonate during a seek operation), when the maximum average settle time exceeds the predetermined threshold value. The disc drive controller further includes a counter coupled to the comparator. The counter monitors and increments a compensation count number by a predetermined compensation count number upon receiving the first command signal from the comparator, and further generates a second command signal to adjust seek profile parameters of the disc drive. Upon receiving the second command signal from the counter, the servo controller adjusts the seek profile parameters based on the compensation count number to eliminate the resonance in the actuator arm of the disc drive. The above steps are again repeated until the compensation count number exceeds a predetermined maximum number. When the compensation count number exceeds the predetermined maximum number, the disc drive is rejected for not being feasible to make anymore adjustments to the seek profile parameters, to eliminate the resonance in the actuator arm. Also included in the disc drive controller is a memory to store the compensation count number, and the threshold value.
Also discussed is a method of adjusting seek profile parameters of the disc drive during a seek operation to eliminate resonance in an actuator arm of the disc drive. Upon receiving a command to seek data from a zone on the disc drive, the disc drive controller checks for a value of a stored compensation count number for the zone in a memory, and at the same time generates a seek profile for the disc drive. Based on the value of the stored compensation count number for the zone, the disc drive controller adjusts the seek profile parameters of the zone in and issues a command to seek data on the disc drive.
Advantageously, the procedure set forth above and the apparatus for implementing the adjustment of the seek profile parameters to eliminate resonance of an actuator arm, allow for more consistent throughput performance from disc drive to disc drive and to reduce production costs by being able to salvage disc drive that would otherwise have been scrapped for having resonance in the actuator arm. Also the above procedure can improve the disc drive acoustic performance by eliminating the resonance in the actuator arm. The above procedure can be incorporated in microcode and used to control the servo circuitry to implement the invention.